Abstract
Abstract. The ASTER Global Digital Elevation Model Version 3 (GDEM v3) was evaluated over the conterminous United States in a manner similar to the validation conducted for the original GDEM Version 1 (v1) in 2009 and GDEM Version 2 (v2) in 2011. The absolute vertical accuracy of GDEM v3 was calculated by comparison with more than 23,000 independent reference geodetic ground control points from the U.S. National Geodetic Survey. The root mean square error (RMSE) measured for GDEM v3 is 8.52 meters. This compares with the RMSE of 8.68 meters for GDEM v2. Another important descriptor of vertical accuracy is the mean error, or bias, which indicates if a DEM has an overall vertical offset from true ground level. The GDEM v3 mean error of −1.20 meters reflects an overall negative bias in GDEM v3. The absolute vertical accuracy assessment results, both mean error and RMSE, were segmented by land cover type to provide insight into how GDEM v3 performs in various land surface conditions. While the RMSE varies little across cover types (6.92 to 9.25 meters), the mean error (bias) does appear to be affected by land cover type, ranging from −2.99 to +4.16 meters across 14 land cover classes. These results indicate that in areas where built or natural aboveground features are present, GDEM v3 is measuring elevations above the ground level, a condition noted in assessments of previous GDEM versions (v1 and v2) and an expected condition given the type of stereo-optical image data collected by ASTER. GDEM v3 was also evaluated by differencing with the Shuttle Radar Topography Mission (SRTM) dataset. In many forested areas, GDEM v3 has elevations that are higher in the canopy than SRTM. The overall validation effort also included an evaluation of the GDEM v3 water mask. In general, the number of distinct water polygons in GDEM v3 is much lower than the number in a reference land cover dataset, but the total areas compare much more closely.
Highlights
The initial version of the ASTER Global Digital Elevation Model (GDEM v1) (Abrams et al, 2010), a joint project of the U.S National Aeronautics and Space Administration (NASA) and the Ministry of Economy, Trade, and Industry (METI) of Japan, was released in June 2009
The Root Mean Square Error (RMSE) is an accuracy metric commonly used for elevation data, and the measured root mean square error (RMSE) for Global Digital Elevation Model Version 3 (GDEM v3) is 8.52 meters
Absolute vertical accuracy can be expressed with a confidence level, in many cases 95%, or referred to as “linear error at 95% confidence” (LE95)
Summary
The initial version of the ASTER Global Digital Elevation Model (GDEM v1) (Abrams et al, 2010), a joint project of the U.S National Aeronautics and Space Administration (NASA) and the Ministry of Economy, Trade, and Industry (METI) of Japan, was released in June 2009. The user community widely embraced the availability of GDEM v1 even though NASA and METI acknowledged it to be a “research grade” dataset that contains anomalies and artifacts that may limit its usefulness for some applications. To address limitations of GDEM v1, NASA and METI jointly developed GDEM Version 2 (v2) (Tachikawa et al, 2011) and released it to the user community in October 2011. In 2015 (for a 2016 release) a third version of GDEM was produced, again taking advantage of additional ASTER scenes (350,000) and further improvements in water body delineation. Use of the same assessment approach previously employed on GDEM v1 and v2 ensures compatibility of the results for comparative purposes
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